Implantable pulse generators are implanted in a formed pocket beneath the skin of a patient. Some pulse generators, such as defibrillators or pacemakers implanted in children, are placed in a pocket formed in the abdominal region of the patient. As is shown in FIG. 1, which illustrates a conventional method of implanting a pulse generator in a patient's torso 120, an electrode lead 80 carries electrical stimulating pulses produced by a pulse generator 110, for example a defibrillator, to a stimulating site 114 on the patient's heart 128. A distal tip portion of the electrode lead is entered into a perforation 138 in a vein (such as the right subclavian vein 122), threaded through the vein and the superior vena cava 126, introduced into the right atrium 130 of the heart 128 and affixed to the stimulating site 114 in the right ventricle 132 of the heart. A proximal end of the lead is tunnelled under the skin from the perforation 138 in the vein 122 to an implantation pocket 115 into which the pulse generator 110 is placed in the patient's abdomen 109. To allow for a patient's common rotation and extension motions occurring during daily life, a clinician will provide some slack in the lead 80 and place the excess lead 80 length in a loop 112 under the patient's skin.
The manner of implantation shown in FIG. 1 has numerous disadvantages. It is well known that an electrode lead tip may dislodge from the heart or that damage may occur to an electrode lead as a result of traction or torsion forces which act upon a lead implanted in this manner. FIGS. 2A and 2B illustrate a conventional lead failure due to kinking. When a patient rotates at the pelvis or extends the upper body, a traction force 116 pulls on and extends the lead 80. The extension of the lead 80 may be sufficient to pull the loop 112 tight, resulting in a kink 118 shown in FIG. 2B. A kink 118 may damage either a conductor internal to the lead or insulation covering the conductor, ruining the functionality of the lead either by decreasing or eliminating the amplitude of a delivered stimulating pulse, destroying the capability of the pulse generator to sense electrical activity of the heart, by causing a significant power drain which shortens the service lifetime of the pulse generator, or by generating an artificial electrical signal (a noise signal) which could be interpreted by the device as a heart signal.
Furthermore, an additional disadvantage of the conventional manner of implanting a lead arises due to the common practice of looping the excess lead length within the body. Looping the excess lead length causes a torsion force to be stored in the lead. Extensions, contractions and flexions of the patient's body place traction forces on the lead which pull and push the lead loops, resulting in changes in the diameter of the loop and the generation of a torque acting on the lead body. FIGS. 3A and 3B illustrate a manner in which traction forces on a lead may result in a propagation of rotational or torsion forces on the lead 80. When a patient contracts the upper body, a compression force 108 may act upon the lead 80 which leads to expansion 119 of the lead loop 112, creating a torque 117 or torsional force which propagates up and down the lead 80. As the lead 80 rotates under such torsional force 117, the lead tip (not shown) will rotate. Over time these forces may tend to cause a helical screw lead tip to unscrew, or may cause other types of fixation devices, such as a tine fixation apparatus, to twist out of position from within the heart.
Although many electrode leads employ coiled wires, which tend to avoid kinking, most lead loops will expand or "pull out" to translate traction forces into torque.
FIG. 4 illustrates an improved conventional manner for implanting an electrode lead 80 which relieves some of the torsion and traction forces on the electrode lead tip at the stimulating site 114 by securing the lead 80 to body tissue near the perforation 138 in the vein into which the lead 80 is inserted. The lead 80 is secured to the body using a suture collar 111, fastened by suture ties 113. The suture collar 111 relieves the torsion and traction forces on the distal tip of the electrode lead 80 at stimulating site 114 merely by transferring and limiting the action of those forces to the location at which the suture collar 111 is placed in the body. These forces are merely moved and not greatly lessened or eliminated. Therefore, the torsion and traction forces will act directly upon the suture collar 111, over time, with the torsion forces tending to weaken the sutures 113 in the circumferential direction and the traction forces pulling and pushing against the sutures in a longitudinal direction. Ultimately, the suture ties 113 may fail and the lead 80 may tear free from the body tissue, nullifying the advantage of securing the lead 80 using the suture collar 111.
What is desired for anchoring an electrode lead to a patient's body, is an apparatus and method which eliminates or greatly reduces the torsion and traction forces acting on the lead. The lead anchoring apparatus and method of the present invention differs from conventional anchoring arrangements by utilizing two interconnected and selectively positioned suture collars to anchor the lead to the patient's body in a manner which reduces or eliminates traction forces that act longitudinally upon the distal portion of the lead.
It follows that the reduction of such torsion and traction forces will prevent dislodging of the lead tip from the heart, since torsion forces tend to unscrew a helical screw lead or twist out tined leads. Furthermore, traction forces weaken the implant by pulling or pushing on the lead tip. In addition, the lead anchoring arrangement of the present invention prevents damage to the lead from kinking, distention or contraction, and prevents dislodging of the suture collar, as well as the implanted lead tip, from the patient's tissue.